Rallying is basically a move command, it is just a move command that focuses on a particular tile

1. Establish a rally point
when you have a unit selected, move over some tile it is NOT on an click the Left thumb stick... this will
establish a rally point
AND
move the unit to that rally point

2. To USE a Rally point
When a unit is selected, keep it over the tile the unit is ON and Left thumb click
This will show you the path to the rally point
Next click either 'A' or Left Thumb Stick to tell the unit to move to ther Rally point.

1. They don't have to be 'reassigned' when you switch production in a city to something you don't want to rally

2. You can use it for armies in the field. time to move every one to the prep point for next assault... every troop begins moveing there as I give the command.. verry nice for the transcontinental war.

So to be clear, the functionality is that you can have a single active rally point in the game at any one time, and to send any unit to that rally point is only a quick couple presses of the thumbstick and then A?

So to be clear, the functionality is that you can have a single active rally point in the game at any one time, and to send any unit to that rally point is only a quick couple presses of the thumbstick and then A?

Pretty much. Once you have established a rally point, double click the left stick to quickly send another unit there. It is actually pretty useful, even if it's not fully automated (i.e. you still need manual input to send other units there).